Xcyloxy-endblocked  diorgano-



3,032,532 ACYLOXY-ENDBLGCKED DIORGANO- PGLYSILOXANES Leonard B. Brunei,Madison, Wis, assignor to Dow Corning Corporation, Midland, Micln, acorporation of Michigan No Drawing. Filed Nov. 9, 1959, Ser. No. 851,518

2 Claims. (Cl. 260-465) This invention relates to acyloxy-endblockeddiorganopolysiloxane compositions useful as intermediates in thepreparation of fluids and rubber-grade gums and to a novel method forthe preparation of such composiitons.

This invention relates specifically to a composition of the formulaAcO(SiR O) Ac in which each R is an organic radical selected from thegroup consisting of monovalent hydrocarbon radicals and halogenatedmonovalent hydrocarbon radicals, each Ac is a saturated aliphaticmonoacyl radical of less than four carbon atoms and n is a positiveinteger greater than nine.

In the compositions of this invention each Ac group can be the formyl,acetyl or propionyl radical. Each R can be any monovalent hydrocarbonradical such as alkyl radicals such as methyl, ethyl, butyl,tertiary-butyl, octadecyl and myricyl; any alkenyl radical such asvinyl, allyl or hexenyl; any cycloaliphatic hydrocarbon radical such ascyclohexyl, cyclopentyl, cyclohexenyl and cyclobutyl; any alkarylhydrocarbon radical such as benzyl or fi-t phenylethyl and any aromatichydrocarbon radical such as phenyl, tolyl, xylyl, naphthyl, xenyl andphenanthryl, R can also be any halogenated monovalent hydrocarbonradical such as chloromethyl, pentafluorobutyl, trifluorovinylchlorophenyl, bromophenyl, a,oc,a-trifluorotolyl, bromoxenyl,chlorotrifluorocyclobutyl, chlorocyclohexyl and iodophenyl.

For the purpose of this invention the polymer size of the compositionscan vary from thin fluids where n has a value of to non-flowing gumswhere n has a value of 10,000 or more. Where n is less than 10,hydrolysis of the acyloxy-endblocked polymers tends to form some cyclicmaterials which are undesirable.

There are two preferred methods for preparing the compositions of thisinvention. One method is fully described in my recently-filed copendingapplication Serial Number 842,586, filed September 28, 1959, andentitled Diorganopolysiloxane Polymerization. This method involves thereaction of a hydroxy-endblocked polymer of the formula HO(SiR O) H witha diacyloxy compound of the formula AcO (SiR O) Ac, where R and Ac areas above defined and m and m are each positive integers, in a mol ratioof 1 to 2 to produce a polymer of the formula AcO(SiR O) (SiR O) (SiR O)OAc where the sum of m +m +m =n. This reaction can be stimulated withheat or can be catalyzed using at least 0.1 percent by weight based onthe weight of the reactants of a non-ionic nitrogen base having adissociation constant of at least 10- e.g. tetramethylguanidine orl,4-bisdimethylaminobutane, or carboxylic acid salt of such a base.

The other method for preparing the compositions of this inventioninvolves the reaction of an organosiloxane with acetic anhydride with orwithout a catalyst. More specifically, this method comprises reacting ata temperature above 50 C. (1) an organosiloxane compound having attachedto each silicon atom from 2 to 3 organic radicals selected from thegroup consisting of monovalent hydrocarbon radicals and halogenatedmo-novalent hydrocarbon radicals and (2) at least one mol per mol of (l)of acetic anhydride, whereby the product has a degree of polymerizationless than that of (1). The organic radicals are more specificallydefined above as R.

3,032,532 Patented May 1, 1932 The organosiloxane compound (1) can be ahexaorganodisiloxane or alinear diorganopolysiloxane endblocked wthorganic radicals or hydrolyzable radicals such as OAc radicals, OHradicals, halogen atoms or hydrocarbonoxy radicals. Where hydrolyzableradicals other than OAc are present, they are replaced by OAc radicalsto form some of the claimed compositions SiOH+AcOAc ESiOAc+AcOHESlCl+ACOAC ESlOAC-I-ACCI E SiOEt+AcOAc- ESiOAc+AcOEt Subsequently,reactions by the method of this invention break down the siloxanelinkages of (l) and form other acyloxy-endblocked polysiloxanes claimedin this invention.

The mol ratio of acetic anhydride to compound 1) determines the amountof molecularsize reduction'which takes place. The mechanism of thisreaction is apparently:

It is evident from this reaction that the composition produced must havea lower degree of polymerization, i.e. fewer siloxane units permolecule, than the original organosiloxane compound.

The method of this invention requires heat. There is negligible reactionat less than 50 C. Generally, this method is ideally run at refluxtemperatures, but higher temperatures can be used with pressure ifdesired. I Mutual solvents such as toluene, xylene andmethylisobutylketone can be present if desired. 1

While no catalyst is necessary, the method of this invention proceedsmore efiiciently in the presence of a boron triacetate catalyst presentin an amount equal to at least 0.5 percent by weight of the reactingcomponents. There is no critical maximum amount of catalyst although theuse of more than 25 percent by weight produces handling problems.Preferably, the boron triacetate should be present in an amount rangingfrom 3 to 10 percent by weight based on the Weight of the reactingcomponents to achieve the best results.

The claimed method is useful not only in producing the claimedcompositions of this invention without undesired siloxane bondrearrangement but in salvaging polysiloxane rubber stocks by providing ameans of breaking down a cured polymer or a high molecular weight guminto usable fluid andgum components.

The compositions of this invention are useful as intermediates in thepreparation of organic end-blocked fluids or high molecular weightcyclic-free polymeric gums of predetermined molecular structure by themethod described in my aforementioned copending application:

The following examples are merely illustrative and are not intended tolimit this invention which is properly delineated in the claims. Allviscosities were measured at 25 C. The symbols Me, Ph and Vi representthe methyl, phenyl and vinyl radicals respectively.

Example 1 IO-grams of B 0 and 350 grams of acetic anhydride were heateduntil the solid phase had disappeared showing the production of borontriacetate. 228.3 grams of hexamethyldisiloxane were then added. Thesystem was refluxed for 72 hours. The reaction product was diluted withcyclohexane, filtered, washed with cyclohexane and fractionated. Theproduct was II MegSiOC CH3 Example 2 8.75 grams of a 5310 cs.hydroxy-endblocked dimethylpolysiloxane, 3.0 grams ofoctamethylcyclotetrasiloxane as a solvent-purging agent, 0.5 gram ofpyridine and 0.5 gram of methylvinyldiacetoxysilane were mixed andheated for 75 minutes at 75 C. The product was stripped and found to bea fluid made up of molecules of the average formula w l t CH C OSIiO(SiMGzOhSiO CH3 Vi Vi in which n was approximately 400.

Example 3 4.82 grams of a 58,800 cps. hydroxy-endblocked 3,3,3-trifluoropropylmethylpolysiloxane, 1.00 gram of pyridine and 1.00 gramof methylvinyldiacetoxysilane were mixed and heated for 3 hours at 70 C.The stripped product was a viscous fluid made up of molecules of theaverage formula 1 1i l i is 01130 OSIKC FaCHzCHzSlJl/IGOMSR 0 CH3 V1 Viin which n was approximately 142.

Example 4 The following hydroxy-endblocked dimethylpolysiloxanes weremixed with acetic anhydride in amounts greatly in exces of 2 mols ofacetic anhy-dride per mol of dimethylpolysiloxane. Pyridine was added toaccelerate the reaction of the silicon-bonded hydroxyl groups with theacetic anhydride. Each mixture was heated for 63.5 hours at 110 C.producing acetoxy-endblocked dimethylpolysiloxanes of the viscositiesshown corresponding to the following average values of n in the formulaSeveral mixtures were made up consisting of 120 grams of 100'cs.trimethylsiloxy-endblocked fluid copolymer of 10 mol percentphenylmethylsiloxane units and 90 mol percent dimethylsiloxane units,4.9 grams of pyridine and 5.4 grams of acetic anhydride. These mixtureswere heated together for the times shown at about 110 C. and allowed tocool after which they were twice rinsed withoctamethylcyclotetrasiloxane and stripped at up to 140 C. and 0.2 mm.Hg. The samples were then titrated for silicon-bonded acetoxy content.

AcO (per- Time (hrs.): cent by wt.) 2 0.0600

Example 6 6.53 grams of acetic anhydride were mixed with grams of a highmolecular weight hydroxy-endblocked3,3,3-trifiuoropropy1methylpolysiloxane gum. The sample was heated 16hours at C. and 72 hours at C. The sample was vacuum stripped for 16hours at about 80 to 100 C. at 1 mm. Hg. The final viscosity of theproduct was 7850 cps. Titration of the acetoxy groups in the productshowed the product to have the average formula Me A00 (C FaOH2CHzSiO)sAcWhere n has an average value of 58.1

Example 7 When a hydroxy-endblocked copolymer having an average degreeof polymerization of approximately 420 and composed of 65 mol percentdimethylsiloxane units, 30: mol percent chlorophenylmethylsiloxaneunits, 3 mol percent dibenzylsiloxane units and 2 mol percentoctadecylmethylsiloxane units is substituted mol per mol for thehydroxy-endblocked dimethylpolysiloxane in Example 2, the resultingproduct is approximately wherein n n n and n have the average values273, 126, 12.6 and 8.4 respectively.

Example 8 When phenylmethyldipropionoxysilane is substituted mol per molfor the methylvinyldiacetoxysilane in Example 2, the product is a fluidmade up of molecules of the average formula d l i l CHaCHzC O SliO(SiMezO)nS[iO 0 01110115 Me Me in which n is approximately 400.

That which is claimed is:

1. A composition of the formula AcO(SiR O) Ac in which each R is anorganic radical selected from the group consisting of monovalenthydrocarbon radicals and halogenated monovalent hydrocarbon radicals,each Ac is a saturated aliphatic monoacyl radical of less than fourcarbon atoms derived from a carboxylic acid and n is a positive integergreater than nine.

2. A method comprising reacting at a temperature above 50 C. (1) anorganosiloxane compound having attached to each silicon atom from 2 to 3organic radicals selected from the group consisting of monovalenthydrocarbon radicals and halogenated monovalent hydrocarbon radicals and(2) at least one mol per mol of (1) of acetic anhydride in contact with(3) at least 0.5 percent by weight based on the total weight of (1) and(2) of boron triacetate whereby the product has a degree ofpolymerization less than that of (1).

References Cited in the file of this patent UNITED STATES PATENTSConstan Oct. 29, 1957 Bailey et al. Oct. 27, 1959 OTHER REFERENCESUNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PatentN0,3,032,532 May 1, 1962 Leonard B. Bruner It is hereby certified thaterror appears in the above numbered patent requiring correction and thatthe said Letters Patent should read as corrected below.

Column 2, line 56,

1eft-hand portion of the formula, for "AcO(SiR O) Ac+3R SiOH- readAC0(SiR O) AC+2R SiOH'- line 58, for the formula "-E (SiR O) -SiR O)read {(SiR O) (SiR O) Signed and sealed this 20th day of November 1962.

(SEAL) Attest:

ERNEST w. SWIDER DAVID LADD Attesting Officer Commissioner of Patents

1. A COMPOSITION OF THE FORMULA ACO(SIR2O)NAC IN WHICH EACH R IS ANORGANIC RADICAL SELECTED FROM THE GROUP CONSISTING OF MONOVALENTHYDROCARBON RADICALS AND HALOGENATED MONOVALENT HYDROCARBON RADICALS,EACH AC IS A SATURATED ALIPHATIC MONOACYL RADICAL OF LESS THAN FOURCARBON ATOMS DERIVED FROM A CARBOXYLIC ACID AND N IS A POSITIVE INTEGERGREATER THAN NINE.